1. Field of the Invention
The present invention relates to a projection exposure lens in a projection exposure apparatus such as a wafer scanner or a wafer stepper used to manufacture semiconductor elements or other microstructure devices by photolithography and, more particularly, to a catadioptric projection optical lens with an object side catadioptric system, an intermediate image and a refractive lens system for use in such a projection exposure apparatus.
2. Related Background Art
U.S. Pat. No. 4,779,966 to Friedman gives an early example of such a lens, however the catadioptric system being arranged on the image side. Its development starting from the principle of a Schupmann achromat is described. It is an issue of this patent to avoid a second lens material, consequently all lenses are of fused silica. Light source is not specified, band width is limited to 1 nm.
U.S. Pat. No. 5,052,763 to Singh (EP 0 475 020) is another example. Here it is relevant that odd aberrations are substantially corrected separately by each subsystem, wherefore it is preferred that the catadioptric system is a 1:1 system and no lens is arranged between the object and the first deflecting mirror. A shell is placed between the first deflecting mirror and the concave mirror in a position more near to the deflecting mirror. All examples provide only fused silica lenses. NA is extended to 0.7 and a 248 nm excimer laser or others are proposed. Line narrowing of the laser is proposed as sufficient to avoid chromatic correction by use of different lens materials.
U.S. Pat. No 5,691,802 to Takahashi is another example, where a first optical element group having positive refracting power between the first deflecting mirror and the concave mirror is requested. This is to reduce the diameter of the mirror, and therefore this positive lens is located near the first deflecting mirror. All examples show a great number of CaF2 lenses.
EP 0 736 789 A to Takahashi is an example, where it is requested that between the first deflecting mirror and the concave mirror three lens groups are arranged, with plus minus plus refractive power, also with the aim of reducing the diameter of the concave mirror. Therefore, the first positive lens is located rather near to the first reflecting mirror. Also many CaF2 lenses are used for achromatization.
DE 197 26 058 A to Omura describes a system where the catadioptric system has a reduction ratio of 0.75 less than /xcex21/ less than 0.95 and a certain relation for the geometry of this system is fulfilled as well. Also many CaF2 lenses are used for achromatization.
For purely refractive lenses of microlithography projection exposure system a lens design where the light beam is twice widened strongly is well known, see e.g. Glatzel, E., Zeiss-Information 26 (1981), No. 92 pages 8-13. A recent example of such a projection lens with +xe2x88x92+xe2x88x92+ lens groups is given in EP 0 770 895 to Matsuzawa and Suenaga.
The refractive partial objectives of the known catadioptric lenses of the generic type of the invention, however show much simpler constructions.
The contents of these documents are incorporated herein by reference. They give background and circumstances of the system according to the invention.
It is an object of the present invention to obtain a catadioptric optical system of new construction principles allowing for large numerical aperture, large image field, sufficient laser bandwidth, solid and stable construction, which takes into account the present limitations on availability of CaF2 in quantity and quality. This holds for a DUV projection lens and gives the basis for a one material only lens for VUV (157 nm).
In order to achieve the above object, according to the present invention, there is provided a projection exposure lens according to one of claims 1 to 7 or any combination of them as claimed in claim 8.
Advantageous versions are obtained when including features of one or more of the dependent claims 8 to 28.
An advantageous projection exposure apparatus of claim 29 is obtained by incorporating a projection exposure lens according to at least one of claims 1 to 28 into a known apparatus.
A method of producing microstructured devices by lithography (claim 30) according to the invention is characterized by the use of a projection exposure apparatus according to the preceeding claim 29. Claim 31 gives an advantageous mode of this method.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.